Centralized traffic controlling system for railroads



Jan. 13, 1948. w. M. BARKER CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed Jan. 21, 1947 2 Sheets-Sheet l h attorney Jan. 13, 1948. w. M. BARKER 2,434,240

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed Jan. 21, 1947 2 Sheets-Sheet 2 Snnentor 11/; 7, 1. flaw/aw,

attorney;

Patented Jan. 13, 1948 CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS William M. Barker, Greece, N. Y., assignor to General Railway Signal Company, Rochester,

Application January 21, 1947, Serial No. 723,285

8 Claims.

This invention relates to centralized traflic control systems for railroads and it more particularly pertains to the selective use of a plurality of line circuits in a centralized traffic control system of the code communication type.

The present invention is particularly applicable to a centralized trafiic control system of the general character disclosed in the patent to W. D. Hailes et al., No. 2,399,734, dated May 7, 1946. A system of this character is generally known as a shunt type system in that continuity is maintained for the entire circuit at all times so that the line wires can be used for telegraph and/or telephone purposes without interruption during the coding operations of the code communication system. The code characters are transmitted from a control ofiice as long or short pulses for the transmission of control codes to the respective field stations along the trackway, and indications as to the conditions of apparatus at the respective field stations are communicated to the control ofiice by code characters obtained by shunting the line wires at the respective field stations for selected long and short intervals, thus requiring only a, single central battery at the control office for energization of the entire line circuit. In such a system, the control office can be connected to the line wires at one end of the equipped territory or at an intermediate point, but in either case distinctive station identification codes must be assigned to the respective stations for the entire system, and stepper units must be provided for the number of stations selecting code characters thus required.

It is an object of the present invention to inductively couple two line circuit portions to provide for end-to-end alternating current continuity for telephone purposes, each portion being selectively isolated with respect to direct current energization when the system is initiated into a cycle of operation for code communication between a field station associated with the other line circuit portion and the control office, thus allowing the use of the same station identification codes for field stations in one circuit portion of the line circuit as in the other circuit portion.

Another object of the present invention is to render the control ofiice response to a field station start of an indication cycle by a station associated with one line portion efiective to isolate the line wires of the other line portion as far as the code communication part of the system is concerned.

Another object of the present invention is to render a particular line portion superior to the 2 other line portion in a case of simultaneous starts of field stations associated with both of such line portions.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings and in part pointed out as the description of the invention progresses.

In describing the invention in detail, reference is made to the accompanying drawings in which Figs. 1A and 113 when placed one above the other show one embodiment of the present invention in which a control office is located at an intermediate point with respect to a line circuit having associated therewith field stations disposed at various points along the centralized trafiic control system.

For the purpose of simplification of this disclosure of the present invention reference is to be made to the above mentioned Hailes et a1. Patent No. 2,399,734, dated May '7, 1946, for a detailed description of the operation and organization oi the code communication apparatus.

To facilitate readily identifying parts of that patent with similar apparatus shown in the present disclosure, corresponding letter reference characters have been assigned to corresponding parts of the two disclosures and certain of the numerical reference characters used in the Hailes et a1. patent have been used in the present disclosure.

The illustrations have been arranged as conventional schematic wiring diagrams for facilitating the disclosure of the present invention as to its mode of operation rather than for illustrating the specific construction and arrangement of parts that would be employed in practice. The symbols and are employed to indicate the respective positive and negative terminals of batteries or other suitable sources of direct current in the conventional manner.

The relays LV, SC, SB, SA, LET, OR, C, E, CF, LCSR, and LCSL are shown only in block form as the control circuits of these relays can be provided as shown and described in the above mentioned Hailes et al. patent. In that patent the relay LCS is to be considered as corresponding to the relay LCSR of this disclosure or the relay LCSL, and it will be more readily apparent as the description progresses as to the reason for two of such relays in this disclosure as compared to the single relay LCS employed in that patent.

With reference to Fig. 1A, the general organization of the system is such that the line wires LI and L2 constitute line portion A extending to the left of the control ofilce, and the line wires L3 and L4 constitute line portion B extending to the right of the control office. It is assumed that the line wires are used for telephone and/or carrier purposes, and therefore the line portions A and B are coupled to the control otfice by a suitable high-passcoupling transformer to allow passage of telephone messages from one line. to the other but to effectively isolate the two line circuits with respect to code communication except as such two line circuits areconnected together with circuit selections at the control-emcee; At the extreme ends of the line portions A and B, the respective telephone apparatus-iscoupled'by a suitable high-pass filter transformerpto: the respective line portions A and B.

The code communication system is considered to be at rest when the system is inactive because of there being no controls or indications tobe communicated between the control oifice and the respective field stations. It is this condition that is illustrated by the positions-of the contacts in the drawings, and at such times the line battery LB is efiective to energize both the line circuits A and B. The positive-terminal of the battery. LB is connected to the line wire L2 by acircuit including front contact ill of relay OR, back contact ll of relay C, back contact l2 of relay CF, back contact l3 of relay SRR andlow-pass filter coils, l4 and I5, to line wire L2.

Similarly the positive terminal of the battery LB is connected to the line Wire L4 by a circuit including front contact Iii-of relay OR, back contact ll of relay C, back contact -l2 of relay CF,

back contact iii of relay SRL and low-pass filterlow-pass filter coils 22 and 23, to the line wire LI. Similarly the negative terminal of the battery LB is connected to the line wire L3of line B by the circuit including the winding 24 of the impulsetransformer TR, limit resistor LRZ, back contact 25 of relay CF, back contact 26 of relay SRL, and low-pass filter coils 21 and 28, to the line wire L3 of line B.

The polar responsive relays FL and F are asso-' ciated with the respective lines A and B-tobe responsive to changes in the energization of the windings of the respective transformers TL and TR with which such relays are associated. In this way such relays are responsive to shunts applied to the respective line circuitsand in addition the relays F and FL are subject to-local energization at the control ofice.

For purposes of description of the present invention, the energizationof the line circuits as described above is considered as the positiveenergization of the line circuitwhen the positive terminal of the battery LB is connected to the lower line wires L2 and L4 respectively. Each line circuit is pole changed under certain conditions of operation to a condition of negative energization as will be hereinafter considered.

Having thus described the general organization of the apparatus-employed in this embodh ment of the present invention, further descrip-' tion of the system will be set forth-with respect to the mode of operation of the system :under certain typical operatingconditions.

Operation-The general organization; of ;the

; communication system is suchthat, during; a pe-.

4 riod of rest, lines A and B are both energized with a positive polarity so as to condition the line circuits to permit a field start by any one of the field stations by the shunting of its associated line circuit for initiating an indication cycle. The initiation of a control cycle, on the other hand, is effected by the opening of the line circuit.

When a cycle of operation is initiated there is a conditioning period during which the apparatus at the control office and at the field stations relativev to cycle demarcation and other features is rendered eifective. Following the conditioning period, code pulses are transmitted having their characters defined by their relatively long or short duration. The first group of pulses transmitted is used for station identification in either a control or an indication cycle, and the last group of pulses is used for defining controls in the case of a control cycle, and for defining indications in the case of an indication cycle. After the controls or indications are transmitted the system enters a clear-out period during which the restoration of stepping relays and other relays that v are active during a cycle is efiective to allow the system to be restored to its period of rest.

The control ofiice has superiority over the field stations in that it applies the positive polarity from becoming efiective, and in case any field starts have become effective, the conditioning pe riod is made long as compared to the conditioning period of an'indication cycle in order that the-control office may overrule a simultaneous 40 20 of relay CF, back-contact 2| of relay SRR and start which has been initiated by a field station.

The initiation of a control cycle is eiTected in response to the manual designation of controls to be transmitted to a particular field station by the actuation of levers provided for such station on a suitable control machine as disclosed in the above mentioned Hailes et al. patent, and in response to the conditioning of such levers, and

the actuation of a start button, control storage and code determining relays are picked up for the transmission of the designated controls, only one Fig. 2C.

Acorresponding mode of operation is contemplated for the system according to the present invention with a similar circuit structure for ini- -tiation of a control cycle except that two relays LCSR and LCSL (see Fig. 1B) are provided in place of the single relay LCS in Fig. 20 of the 65, above mentioned Hailes et al. patent, each of such relays being controlled in a manner corresponding --to the relay LCS of that patent except thatits control circuit is limited to association with code determining relays LC provided for field stations associated with a single line circuit.

words the relay LCSR of the present disclosure In other --is energized in. series with windings and front contacts of relays LC for the respective field stations of line B corresponding to the circuit for a the relay LCS of the above mentioned Hailes et and LC3 of that patent are both associated with field stations connected to line B. Similarly the relay LCSL is energized by a circuit including windings and front contacts of relays LC for the respective field stations of line A by a, circuit structure corresponding to that provided in the above mentioned I-Iailes et al. patent for the relay LCS, if it is assumed that the relays LCZ and LC3 of that patent are both associated With field stations connected to line A.

To consider more specifically the mode of operation of the system according to the present invention during a control cycle, it will be assumed that an operator designates a control for transmission to a field station associated with line B, such as the station No. IR, and in response to such designation it will be assumed that the relay LCSR is picked. up in a manner which has been described by the energization of a circuit similar to the circuit provided for the energization of the relay LCS of the above mentioned Hailes et a1. patent. Assuming the code communication apparatus to be in a state of rest at a time when the relay LCSR is picked up, the picking up of that relay is efiective to cause the picking up of the relay C in a manner corresponding to the manner in which the relay C is picked up in the above mentioned Hailes et al. patent in response to the picking up of the relay LCS of that patent.

In response to the picking up of the relay C at a time when the relay LCSR is picked up, a circuit is closed to cause the picking up of the relay SRR. Such circuit extends from including front contact 29 of relay C, front contact 30 of relay LSSR, back contact 3! of relay SRL and winding of relay SRR, to Upon the picking up of the relay SRR, a stick circuit is established for that relay to maintain it picked up throughout the control cycle. Such stick circuit extends from including front contact 32 of relay SA, front contact 33 of relay SRR, back contact 3| of relay SRL and winding of relay SRR, to It is thus insured that the relay SRR is maintained picked up throughout the cycle, irrespective of anything which may happen to its pick-up circuit. Such relay also opens the circuit for the relay SRL at back contact 34 to insure that relay SRL is maintained dropped away throughout the control cycle.

The picking up of relay SRR isolates line A from line B, and also from the line battery LB, by the openin of back contacts. Thus by deenergizing line A, it is provided that the energization of a positive polarity is removed from that line circuit, thus preventing field starts from becoming eifective for field stations associated with that line circuit. Although the code communication apparatus at each of the field stations of line A goes through a conditioning period, it also goes through a, clear out period because of the sustained deenergization of that line. The decay of flux in the transformer TL due to the opening of the circuit connected to line A induces a voltage in the secondary winding 35 of such transformer in a direction to maintain the relay FL in its normal position with its contacts actuated to their right-hand positions.

The picking up of relay C initiates the conditioning period for line B by opening the circuit connecting the positive terminal of the battery LB (see Fig. 1A) to the line wire L4 at back contact H. The closure of front contact H of relay C applies a shunt across the line wires L3 and L4 of line B through the drainage resistor DRI. Such shunt extends from line wire L3 including low-pass filter coils 21 and 28, back contact 26 of relay SRL, back contact 25 of relay CF, drainage resistor DRI, back contact 36 of relay E, front contact ll of relay C, back contact l2 of relay CF, back contact l6 of relay SRL and low-pass filter coils l! and I8, to the line wire L4. The picking up of relay C also opens the circuit for the upper winding of relay F (see Fig. 1B) and closes a shunt across the secondary winding of the transformer TR through contacts 358 and 359 of relays C and SC respectively. The shunt is maintained throughout the cycle by the closure of front contact 360 of relay SA.

The relay F has its lower winding energized in response to the picking up of the relay C with a polarity to operate the contacts of that relay to their left-hand positions by a circuit extending from including front contact 68 of relay C, back contact 69 of relay E, and lower winding of relay F, to

In response to the actuation of the contacts of relay F to their left-hand positions, the relay OR is deenergized, and the relays LET, SA, SB and SC are successively picked up as disclosed in the above mentioned Hailes et al. patent.

The relay OR because of its slow drop away characteristics does not become dropped away until the relay SB is picked up, and thus the circuit including back contact ID of relay OR and back contact3l of relay SB for precharging the impulse transformer TB is not closed until the end of the cycle, at which time the relay SB is dropped away prior to the picking up of the relay OR. Similarly the back contact 38 of relay SB is opened before the closure of back contact 39 of relay OR during the conditioning period in the precharge circuit for the impulse transformer TL associated with line A to provide that such precharge circuit is closed only at the end of the cycle when relay SB becomes dropped away prior to the picking up of the relay OR.

The line B is maintained deenergized until the conditioning period is terminated upon the picking up of relay E in response to the dropping away of relay LET as disclosed in the above mentioned Hailes et a1. patent and as indicated in the sequence chart of Fig. 7A in that patent.

The picking up of relay E at the end of the conditioning period closed a circuit to apply a pulse of positive polarity to line B. The negative terminal of the line battery is connected to the line wire L3 by a circuit which has been described, and the picking up of relay E is effective to connect the positive terminal of the battery LB to the line wire L4 through front contact 36 of relay E, front contact H of relay C, back contact l2 of relay CF, back contact l6 of relay SRL and low-pass filter coils l1 and I8 to line wire L4. The opening of back contact 36 of relay E removes the drainage shunt that has been applied across the line wires L3 and L4.

After the timing of the first pulse of the control code has been completed at the control oflice, the relay E is dropped away, and the dropping away of that relay opens the line circuit at front contact 36 and reconnects the drainage resistor DRI across the line wires L3 and L4. After the completion of the timing of the o period following the first on period, the relay E is again picked up to open the circuit at back contact 36 for the drainage resistor DR! and close a circuit which has been described at front contact 7 ?-.38:tofapply energy of: a; positive polarity .tcrthe :Ijine B fortthe second pulse of the code.

The: stepping progresses to provide the re- :cquired numberiof code characters in a manner :rcorresponding to that which, has been described ffor. the first :c'ode characters until th designated ::controls have been transmitted At the end of :'the1last.on' period the system enters; a clear- LOllt foif'period during which time the relay F :thas'itscontacts actuated to their left-hand po- :.?sitions by a: circuit which-has been described for :the'lower windingof'the relay F, closed at back :rcontact69 of the :relay E (see Fig. 1B) upon the -cdropping away 'ofthat relay at the end of the last "on period. Th relay LCSR is dropping.

. awaycupon the picking 'up .of the laststep relay, and thedropping away'of relay LCSR, by open- .y'ing' front contact 30in the circuit for relay SRR, allows relay SRR to be dropped away when its e stick circuit is opened at front contact 32 of relay SA toreestablish the line circuit connectionsfor line A at back contacts, I6 and26 (see Fig. 1A). "The line battery LB; however, does not yet have its positive terminal connected to the line'circult because the picking up of the relay OR is 4 essential to the closingof that circuit and is also essential to connecting the positive terminal of the battery LE to the line wire L4 of the line B.

"The relays LET, SA, SB, and C are successively dropped away and the dropping away of '--relay SB, with the relay SA dropped away and i the relay SC still picked up, closes a circuit by -which the center winding of relay F (see Fig. '1B) isenergized with a polarity to actuate its contacts to their right-hand positions. Such circuit extends from including back contact 483 of relay SA, front contact 484 of relay SC,

back contact'485 of relay SB and center winding of relay F to Upon the picking up of relay Fthe relay OR is energized and in re- --sponse tothe picking up of that relay the circuit for the relay SC is opened to cause that relay to be dropped away.

I Drainage of the line circuits at the end of the cycle, after relay C has dropped away and before "relay OR is picked up, is accomplished "through a circuit including resistor DRZ, back contact-46 of relay OR, and back contact II of relay C.

Because of the relay SB having been dropped away prior to the'picking up of relay OR, a circuit is closed at such time for energizing the primary winding 24 of the transformer TR through the precharg resistor PR2. Such circuit extends from the positive terminal of the battery LB, including back-contact II! of relay OR, precharge resistor PR2, back contact '31 of relay SB, limit resistor LR2- and primary winding 24 of trans- T former TR, to the negative terminal of the battery LB. Similarly-the primary winding I9 of .the transformer TL'is -precharged at the same -tim by. a circuit extending from the positive terminal of th battery LB, including back cona-tact 38 of relay SB; precharge resistor PRLback contact 39 of relay ORYIimit resistor LRI, and --primary winding IQ of transformer TL, to the negative terminal of the battery LB.

Theenergization of such precharge circuits ..is.inefiective-.to. actuatethe respective relays F and FL because'the circuits for such relays are opened at that time. More specifically, the relay SA hasdroppedaway at that time to open the circuit for the relay F at front contact 366, and the back contact'359 of relay SC in the circuit for relay'F is not yet closed; The branch of the circuit for the upper winding of the relay F ineluding front contact M of relay LET is opened because the relay LET is dropped away earlier in the clearout period. The windings of the relay FL are disconnected from the secondary winding of the transformer TL during the precharge of that transformer because of the back contact 42 of relay SC being opened. The application of energy to the upper winding of relay FL through a circuit extending from including back contact 43 of relay SB, front contact 42 of relay SC, upper winding of relay FL and resistor 44, to is effective to maintain the contacts of relay FL in their right-hand positions.

Upon the picking up of the relay OR, the clearout period is terminated and the shifting of the make-before-break contacts In and 39 of relay OR connects the line battery LB to the lines A and B to restore the condition of rest of the system. The use of make-before-break contacts of the relay OR maintains continuity in the circuits through the primary windings I9 and 24 of the impulse transformers TL and TR during the shifting from the precharge circuits to the energization of the lines A and B.

A similar mode of operation to that which has been specifically described when considering the transmission of controls to a field station associated with line B is provided for the transmission of controls to a field station associated with line A. It is therefore believed unnecessary for an understanding of the circuit structure and the mode of operation of the system to consider as specifically the transmission of condescribed is effective to cause the picking up of relay C.

The picking up of relay C closes a circuit for the energization of relay SRL (see Fig. 13) extending from including front contact 29 of relay C, front contact 45 of relay LCSL, winding of relay SRL and back contact 34 of relay SRR, to Relay SRL'is maintained picked up during the control cycle by an obvious stick circuit dependent upon front contact 32 of relay SA.

The picking up of relay SRL isolates line B from the line battery LB and from line A by the opening of back contacts I6 and 26. The system then enters a conditioning period corresponding to that which has been described for the initiation of a control cycle, and at the end of the conditioning period the picking up of relay E connects the positive terminal of the battery LB to the line wire L2 by a circuit including front contact 36 of relay E, front contact II of relay C, back contact I2 of relay CF, back contact I3 of relay SRR and low-pass filter coils I4 and I5 last stepping relay during the clearout period, the relay LCSL is dropped away, and the dropping away of that relay by opening front contact 45 allows the dropping away of relay SRL when its stick circuit is opened at front contact 32 of relay SA. Upon the dropping away of relay SRL the closure of back contacts conditions the line B for energization when the system enters a period of rest.

It will be noted that for control cycles there is no condition where starts can be initiated for the two lines simultaneously, even though starts may be stored for transmission to both lines, because of the character of the pick-up circuit for the code determining relays LC as shown in the above mentioned Hailes et al. patent. These relays are energized by a chain circuit which allows only one relay to be picked up at a time, and thus in a double ending system such as herein disclosed all of the field stations of the system, including the stations associated with both lines, have their code determining relays energized by a single chain circuit that allows, the picking up of only one relay at a time, and the superiority of one code determining relay over another is determined by its relative position in the circuit chain.

To consider the mode of operation of the system during an indication cycle, it will be assumed that the line B is shunted by one of the field stations, such as the station IR, having indications to transmit, such shunt being applied when the line circuits are energized with a positive polarity during a state of rest. The application of the shunt causes an increase in current in the portion of line B extending from the field station where the shunt is applied to the control ofi'ice, and including the primary winding 24 of the impulse transformer TR. The increase in flux in the transformer TR. induces a voltage in the secondary winding 66 of that transformer of a polarity to energize the relay F to actuate its contacts to their left-hand positions. The circuit for energization for the relay F under such conditions includes wire ll, contact 48 of relay FL in its right-hand position, upper winding of relay F, back contact 49 of relay LV, back contact 358 of relay C, back contact 359 of relay SC, and wire 50.

In response to the actuation of the contacts of the relay F to their left-hand positions at the beginning of the conditioning period of an indication cycle, the relays CF and LET are picked up, and the relay OR is deenergized so as to become dropped away at a time determined by its slow acting characteristics. In response to the picking up of relay LET, relays SA, SB, and SC are successively picked up and the relay E is picked up in response to the picking up of the relay SA. This mode of operation completes the conditioning at the control office, but the conditioning period is terminated by the field station which is applying the shunt, as such station is doing the transmitting. The pickin up of relay LET at the beginning of the conditioning period applies a shunt across the secondary winding of transformer TR through back contact of relay SB during the shifting of polarity upon the picking up of relay CF so as to render relay F non-responsive to such shift in polarity.

It will be noted that the picking up of relay LET at the beginning of the conditioning period in response to the shifting of the contacts of relay F is efiective to open the circuit for the wind ings of relay FL at back contact 50, and thus 10 prevent actuation of relay FL upon the shifting of relay CF. Although relays CF and LET become energized at the same time, relay CF is slightly slower acting to allow relay LET to be picked up first. I

The picking up of relay CF in response to the shifting of the contacts of relay F pole changes the line circuit at contacts I2 and 25 for conditioning the line circuit to lock out any subsequent field starts that may occur at other field stations of line B during the cycle of operation in a manner fully described in the above mentioned Hailes etal. patent. In response to the picking up of the relay CF, the relay SRR (see Fig. 1B) is picked up for isolating line A from line B and from the line battery LB as selected by the right-hand position of the contacts of the relay FL. Such circuit extends from including front contact 5| of relay CF, contact 52 of relay FL in its right-hand position, back contact 3| of relay SRL and winding of relay SRR, to Upon the picking up of relay SRR, the opening of back contacts [3 and 2| iso.ates line A from line B and from the line battery LB for the remainder of the indication cycle. It will be readily apparent that the indication cycle progresses as fully described in the above mentioned Hailes et al. patent, entering a clearout period at the end of the cyc.e. At the beginning of the clear-out period the relay F is energized with a polarity to actuate its contacts to their left-hand positions, and subsequently relays LET, SA and SB are successively dropped away. Relay F has its contacts actuated to their right-hand positions upon the dropping away of relay SB through a circuit including back contact 483 of relay 5A, front contact 484 of relay SC and back contact 485 of relay SB. In response to the shifting of the contacts of relay F to their right-hand positions, the relay OR is picked up to mark the beginning of a period of rest and cause the dropping away of relay SC.

The dropping away of relay CF during the clearout period is effected in response to the dropping away of the relay SA and the opening of front contact 5| of such relay CF is eiiective to cause the dropping away of relay SRR to restore the back contact l3 and 2| in the circuit for line A to their normally closed positions. The picking up of relay OR at the end of the clearout period restores the normal conditions of energization of a positive polarity to lines A and B in accordance with the relay CF having been dropped away to close its back contacts 28, I2 and 25. It will be readily apparent that the impulse transformers TL and TR are precharged during the clear-out period in a manner corresponding to that which has been described when considering the mode of operation of the system during a control cycle.

To consider the mode of operation of th system for transmission of an indication cycle by a field station associated with line A, it will be assumed that, when the system is at rest, a shunt is applied by a field station associated with line A such, for example, as station IL, such shunt being eifective to increase the flux in the impulse transformer TL to apply energy to the windings of the relay FL with a polarity to actuate the contacts of that relay to their left-hand positions. The circuit by which relay FL is energized under such conditions extends from the righthand terminal of the secondary winding 35 of the transformer TL including wire 53, back contact 50 of relay LET, lower winding of relay FL, upper 11 winding ,of-nrelay FL, back contact ,42, of re1ay,SC, andwi fe t the lefthand. terminalv of the secondary winding 35 -of transformer The windings of therelay FL are poledin COIIC',

spondence to actuate the contacts of ;,tha t, .elay 5 p to their left-hand positions in response to an increasein the energization of theprimary Winding of the impulse transformer TL.

The relay FL in actuating its contacts to their left-hand positions close a circuit to energize the relay F with a polarityto actuate its contacts to their left-hand positions to thereby initiate the conditioning of the, cycle at, the control ofice. The lower winding of relay F is energized under such conditions by, a circuit ex-, tending from including back contact 55.0f relay SC, contact 56, of relay FL in its left-hand positionandlowerwindingof relay.F, to

It will be, readily apparent that the actuation of the contacts of relayF to their left-hand posi-, tions initiatesthe sequence ,of operation during the conditioning period corresponding to the sequence of operation which hasbeen specifically described with reference to the transmission of an indication cycle by a field station associated 25, with line B.

The actuation of;the contacts of relay.FL to their left-hand positions. also selects a circuit for the energization of relay SRLto isolate line B from line A and from the line battery Such circuit extends from including front contact.5l of relay CF cQntactSLof relay FL in its left-hand .position, winding of -relay. SRL and back contact 34 of relay SRR, to The picking up of relay .SEL opens the connectionofline 5., B to the line battery LB,.and .to the line A, at. back contacts I6 and 26. The picking up of relay CF during the conditioning .periodin response to the shifting of the contacts of relay.F to their left-hand positions, in. addition to-. polechange ing line A, opens the circuit for the impulse transformer TL and the limit resistor at back. contact. 20 and closes a circuitatfront contactby which the negative terminal of the line battery LB is connected to-the linewireLZ of line .A through the primary-winding-M of the impulsetransformer TR and through the limit resistor A LRZ. The positive terminal of the line battery LB is connectedto-line wire-Ll throughfront contact 2'0 of relay CF.

This .mode. .of operation --is accomplished in order that the relay F may be rendered directly responsive. to. the shunting and unshunting of line A during the -indicatiomcycle ratherthan require that such relayrepeat-th relay FL. 7 In 65 other words, the relayFL-is used-only to-initiate the cycle, and afterthecycle is once initiated and line B is isolated, the. relay F is directlyre sponsive to the. code characters asapplied to line A by the field station doing the transmitting It i thus provided that .the indication cycle of operation progresses-in a mannercorresponding to that which has-been'described specifically for I the transmission duringan indication cycle initiated by a field station associatedwithline B.

In case of simultaneous starts by field stations associated withboth lines A and .B, the'field station associated with line A is always superior to the station associatedlwithlineB. Thisis true because the contacts of-relay FL select as-to which of the line circuits is to be isolated, and the energization of.relay.FL in response toa field start by a station associated. with line A selects that line B is to be isolated,.irrespective-ofthe simultaneous action,of...the contacts of relay- F in response to;th e;shun ting of lineB.; The picking up of relay LET just, prior to the picking up of relay CF opensthe circuit for relay FL to determinethat no field; start-subsequent to that" time can act upon thelfelay FL.,

It will be noted that although .theimpulse transformer TR is used for stepping at the con-,1

trol ofl'ice duringanindication .cycle transmitted by a field station associated with either line cir,-,

cuit, such transformer, and the limiteresistorLRZ,

at no time carries-theloadof :bothlinecircuits.

This is truebecause wheneverboth line A and line B are energized at the sametime as, during a period of rest, veachjline circuit includes the.

primary winding of itsgrespective impulse trans: former and limiting resistor only; and thus the sensitivityof an impulse transformer to. a shunt applied across its line .circuitiscomparable to the sensitivity of that transformer in a system in which there is no other line circuit involved.

' It is thereforeprovided by this, arrangement, that the size of the linewires required,,and the line battery voltage, for each linecircuit need be no greaterthan would berequired if thatline cir-. cuitwere the only'line circuit included .in the. communicationsystem,as, compared to the size of line wires and the line battery voltage that.

plied to the. specific. form shown toimeet they requirements of practice, withoutin any manner departing from the spirit orscopezofthe present invention, except, as limited .by. the appending claims.

What I claim is:

1. Ina centralized: traflic control systemfor railroads, a linev circuit maintaining end-to-endcontinuity at all times for alternating current communication purposes, said linecircuit comprising twov line portions inductively coupled at an intermediate control-oflicethrough a high-- pass filten-a plurality-of field stationsassociated witheach line circuit portion, each-field station being effective at times-to apply a shunt across its associated line portion through a low-pass filter, a-source of-direct 'current at said control-- office normally. effective-to energize bothof said line-portions, and meansat-said-control oflice responsive to theshuntingofone-of-said line Dortions by one-of-said field stations-for isolating the other of said lineportionsforthe duration of a cycle of operation of the system;- 1

2. Ina centralized traflic control system having a plurality of field stations-connected at various points totwoline-cirouits extending in different=directions from a-contro1-office,- each of-- said field stations being-at times rendered -efiec-- tive to shunt its associated line circuit for initiating a cycle of operation for-thetransmissiom of indications :from-that station,-eircuit means including a single source of energyat the control office normally-efiective when-the system-is at restto energize -eaeh of sa i d- 1ine" circuits; and I electro-responsive--means-at the-control office distinctively responsive as to which of said line circuits is shunted by a field station when the system is at rest for disconnecting the other of said line circuits from said source of energy at the control ofiice for the duration of a cycle of operation of the code communication system, whereby a field station start automatically registers with which line circuit that field station is associated and thus allows the use of the same station identification codes for stations associated with different line circuits.

3. In a centralized tramc control system of the character described for communicating indications over line circuits extending in different directions from a control ofiice, a single source of energy for the energization of said line circuits, an impulse transformer for each of said line circuits, circuit means at the control office for connecting said line circuits to said .source of energy contemporaneously when the system is at rest but isolating said line circuits during a cycle of operation in response to a shunt applied across one of said line circuits, said circuit means including a winding of said transformer in series with said source of energy and its respective line circuits only, whereby the load applied by one line circuit when the system is at rest has no efiect upon the sensitivity to shunts of the impulse transformer of the other line circuit.

4. In a code communication system of the character described, a line circuit extending throughout a stretch of railway track maintaining continuity end-to-end for alternating current at all times, said line circuit being divided into two portions with respect to direct current continuity at an intermediate control office, such portions being inductively coupled through a highpass filter, a single source of direct current energization at said control ofiice normally connected to both of said line portions through a low-pass filter, means for initiating the system into a cycle of operation for the transmission of controls to a field station associated with either of said line portions, and means effective when a control cycle is initiated for transmission to the field station associated with one line portion for isolating the other line portion from said source of energy for the duration of the cycle, whereby the same station selection codes can be used for field stations associated with one line portion as those used for field stations associated with the other line portion.

5. In a centralized trafiic control system for railroads comprisin a plurality of field stations connected at various points to each of two line circuits extending from a control office, each of said field stations being effective at times to shunt said line circuit, a single source of energy at the control office normally effective to energize both of said line circuits, electro-responsive means at the control ofifice associated with each of said line circuits and responsive to a shunt applied to its associated line circuit, and isolation means actuated in response to said electro-responsive means for each line circuit for isolating the other of said line circuits from said source of energy for the duration of a cycle of operation of said system, said isolation means being effective for the isolation of a given one of said line circuits in preference to the other of said line circuits in case of said electro-responsive means being simultaneously responsive to the shunting of both of said line circuits.

6. In a centralized trafiic control system of the character described, a line circuit extending 14 throughout the length of a stretch of track and maintaining continuity at all times for alternating current end-to-end communication, said circuit being divided into two portions with respect to direct current continuity by a high-pass coupling transformer at an intermediate control ofiice, a field station associated with each of said line portions effective at times to apply a shunt across its associated line portion through a lowpass filter, a single source of energy at said control omce normally connected to both of said line portions, electro-responsive means at said control oflice associated with each of said line portions and responsive to a shunt applied to that line portion, and isolation means at the control otfice responsive to said electro-resnonsive means for each line portion for isolating the other line portion from said source of energy for the duration of a cycle of operation, said isolation means being eifective for the isolation of a pre-determined one of said line portions in case said electro-responsive means is simultaneously responsive to both line portions.

7. In a centralized trafiic control system for railroads, a plurality of field stations connected at various points to each of two line circuits extending from a control office, each of said field stations being effective at times to shunt its associated line circuit, a source of energy connected to both of said line circuits when the system is at rest, electro-responsive means associated with each of said line circuits when the system is at rest so as to be responsive to the shunting of that line circuit, means responsive to said electro-responsive means for either of said line circuits for initiating an indication cycle at the control ofiice and isolating the other line circuit from said source of energy for the duration of the cycle thus initiated, and means effective when an indication cycle is initiated for rendering said electroresponsive means for a particular one of said line circuits responsive to line circuit shunts of the field station transmitting irrespective of with which line circuit that field station is associated.

8. In a centralized traffic control system having two line circuits extending from a control ofiice and a plurality of field stations connected to each line circuit, each of said field stations being effective at times to shunt its associated line circuit for selected long and short intervals for transmitting indications to the control ofiice during a cycle of operation, a source of energy connected to both of said line circuits when the system is at rest, impulse transformers having their primary windings connected in series with the respective line circuits when the system is at rest, electro-responsive means for the respective transformers energized by the secondary windings of such transformers and responsive to the shunting of the line circuit with which that transformer is associated, and means responsive to said electroresponsive means associated with either of said transformers for initiating an indication cycle, said means being effective when the cycle is initiated to isolate the line circuit not involved in the shunt which has been efiective to initiate the cycle, said means providing that a particular one of said transformers is energized in response to field circuit shunts after one line circuit is isolated irrespective of to which line circuit the shunt is applied by the field station doing the transmitting.

WILLIAM M. BARKER. 

